Epoxy resins by their very nature are generally chemically resistant and have utility as coatings, encapsulating agents and composite matrices. Even so, the properties of epoxy resins are also affected by the type of curing agent used for curing the polyepoxide. Aliphatic and aromatic polyamines have been used in the past for curing epoxy resins. Cycloaliphatic amine curatives although permitting rapid, subambient and low temperature cures are often used for elevated cure cycles. A problem with low temperature cure with cycloaliphatic amine based curatives is that the amines often leave residual NH functionality in the cured epoxy resin which may react with ambient carbon dioxide to form surface carbamates. These carbamates lead to water spotting and poor interfacial adhesion and, as a result, the resins may be unsuitable for subsequent coating and architectural applications. Although elevated temperature cure with cycloaliphatic amine based curatives can reduce the possibility of amine exudation in the final product it can also lead to temperature excursions causing charring, degradation and vitrification. Thus, it is important in elevated temperature cure that the conditions are controlled to effect substantially complete cure and minimize the possibility of amine exudation while achieving commercially acceptable performance properties within as short as time as possible.
Representative patents which describe epoxy resins and the utilization of cycloaliphatic amines as curatives are as follows: U.S. Pat. No. 2,817,644 discloses the production of polyepoxides from glycidyl polyethers or polyhydric phenols and curing these polyepoxide resins with hydrogenated aromatic primary and/or secondary amines. Cure can be effected at temperatures ranging from about 15.degree. to 280.degree. C. Small castings are cured for about two hours at 80.degree. to 100.degree. C. and then post-cured for an additional two hours or so at 140.degree. to 225.degree. C. Examples of hydrogenated aromatic amines include p,p'-diaminodiphenylmethane (PACM); hydrogenated p-phenylenediamine; hydrogenated meta-phenylenediamine and hydrogenated benzene triamine.
U.S. Pat. No. 3,658,728 discloses a process for preparing moldings from polyepoxides and polyamines wherein a liquid polyamine/alkylphenol adduct is cured. Examples of polyamines suited for effecting cure of the polyepoxide resin, include aliphatic, cycloaliphatic, aromatic and heterocyclic polyamines. Cycloaliphatic polyamines such as diaminocyclohexane, 4,4'-diaminodicyclohexylmethane, and 2,2-bis-(4-amino-dicyclohexyl)propane are shown. The Patentees disclose curing glycidyl ethers of polyphenols using 4,4'-diaminodicyclohexylmethane at temperatures of 60.degree. C. for about 15 hours.
U.S. Pat. No. 5,264,501 discloses curing epoxide resins utilizing bridged cycloaliphatic diamines. The cure cycle disclosed for curing the epoxy resin involved an initial curing of two hours at 80.degree. C., followed by 3 hours at 150.degree. C. Cycloaliphatic amines tested include: dimethylbicyclohexylamine, methylenedi(cyclohexylamine) or PACM and dimethylmethylenedi(cyclohexylamine).
Japanese Publication 53-9639 discloses a hardenable epoxy resin composition, the hardener generally consisting of a hydrogenated aniline/formaldehyde condensate. An elevated temperature cure consisting of two hours at 70.degree. C. followed by five hours at 120.degree. C. was used.
U.S. Pat. Nos. 4,226,737 and 4,321,353 disclose epoxy curatives which are methylene bridged polycycloaliphatic polyamines represented by the structural formula: ##STR1## wherein x and y are from 0-2 and the sum of x plus y is from 1 to 4. Typically the curative consists essentially of 50 to 75% of the methylene bridged tricyclohexyltriamine and from 15 to 30% of the tetracyclohexyl tetramine.
U.S. Pat. No. 3,629,181 discloses various cycloaliphatic and cycloaliphatic-aliphatic di-primary amines for use in preparing adducts as curing agents for polyepoxide resin systems. Representative amines include 1,4-diamino-3,6-diethylcyclohexane; 2,2-di(4-aminocyclohexyl)propane which is commonly referred to as hydrogenated bisaniline A and 3-aminomethyl-3,5,5-trimethyl-1-cyclohexylamine, which is commonly referred to as isophoronediamine.
U.S. Pat. No. 4,946,925 discloses various bridged bis(cyclohexylamine) derivatives as curing agents. Each cyclohexylamine group has two alkyl groups, where the alkyl groups are in the 2 and the 5 positions and the amine groups are in the 4 position. Specific curing agents include 2,2',5,5'-tetramethylmethylenedicyclohexylamine and 2,2',5,5'-tetraethylmethylenedicyclohexylamine.
U.S. Pat. No. 5,280,091 discloses the cure of epoxy resins using a mixture methylene bridged poly(cyclohexyl-aromatic)amines. Cure is effected at 80.degree. C. for 2 hours followed by reaction at 150.degree. C. for 3 hours.